Kenneth's long-range, last-gasp intervention in the Clydesdale Bank Premier League encounter came after he was introduced 20 minutes from time, despite suffering a dead leg in his side's midweek Scottish Cup tie, to add stability to a visiting side which had been reduced to nine men.
The United manager said: "Garry failed a fitness test at Tannadice at 9am but I told the physio to put him on the bus anyway as we didn't have any other players. He was out warming up for the first time when Jon Daly was sent off and we had to use him. I didn't expect him to score our goal but he struck the ball beautifully. He should do it more often!"
Conor Sammon had opened the scoring for the hosts in the first half, and after the break, Alexei Eremenko was sent off for retaliating to a Scott Robertson foul.
Robertson and captain Jon Daly were both booked for the incident, and each received a second yellow card within the next 11 minutes.
Houston said: "When Eremenko was sent off, I thought we'd get an opportunity to get a second striker on, but as I was in the process, Robertson got a second yellow; with his experience he shouldn't get too tight to the player and has to be 100% sure he's going to get the ball.
"I thought the second red card was very harsh. Daly was booked first for running 70 yards to get involved, but as the captain you ask him to separate people, and for the second one [raising an arm] he never touched the boy, so I was disappointed with that.
"This is the fifth away game this season where we've scored a last-minute equaliser -it shows great character and that we don't give up easily, and I thought it was a merited draw.
"I thought the first half was pretty even and the best chance fell to David Goodwillie, which on another day would hit the post and bounce for Scott Robertson to tap in.
"I was disappointed to be 1-0 down at half-time, but I'm delighted we got the goal; Mixu (Paatelainen) will be disappointed that they didn't keep the ball that well in the latter stages as if they had we'd probably have been chasing shadows."